Photographic recording by electric discharge



Feb. 19, 1929.

A. G. COOLEY PHOTOGRAPHIG RECORDING BY ELECTRIC DISCHARGE Filed Dec. 11,1924 K g 7" ,WvM

Patented Feb. 19, 1929. y 1 UNITED STATES PATENT OFFICE.

AUSTIN G. COOLEY, or CAMBRIDGE, mAssAonUsn'rrs, AssmNoR r FORTmNmEonn-nonmmn'rns TO CHARLES c. HENRY, or STRAWBERRY POINT, rowmPHOTOGRAPHIC RECORDING BY ELECTRIC DISCHARGE.

Application filed December 11, 1924. Serial No. 755,339.

This invention relates to photographic reproduction in accordance withprinted matter, pictorial representations, or other photographic orimage likeness, and has for its principal objects to simplify thereproduc ing process, to increase the speed of reproduction, directly toproduce a half-tone effect suitable for reproduction by mechanicalprinting process, simultaneously to make a plurality of reproductions,to enable the process to be performed in a lighted room, to improve thequality of the contrast gradations throughout the high-light, hal toneand shadow areas, and generally to improve the art of photographicreproduction. The invention is particularly applicable to the art ofphoto telegraphy either by Wire or radio, this application of theinvention being disclosed in copending application Serial No. 755,336,filed on even date herewith.

The invention consists in modulating hi ghfrequency oscillations inaccordance with the photographic subject matter, or other sub jectmatter such for example as printed matter, and effecting thephotographic exposure upon an ordinary photographic emulsion or othersuitable receiving or reproducing medium with an electric dischargeproduced by the oscillations. Relative movement may be produced betweenthe discharge and the receiving or reproducing medium, in any suitablemanner. For example, the reproducing medium may be rotated on a drum ordisk and the electrical discharge caused to trace over the medium alongparallel lines constituting a spiral. The electrical discharge ispreferably in the form of corona discharge which pulsates at apredetermined frequency,

either ceasing entirely between beats or decreasing to an intensity solow as to afiect the reproducing medium little if any, thereby forming asuccession of dots or short dashes on the medium. The beats, which aremodulated in accordance With the subject matter, are preferablyimpressed upon high-frequency oscillations which are adapted to producethe corona effect Without disruptive discharge.

For the purpose of illustration one concrete embodiment of the inventionis illustrated in the accompanying diagram in Which the sensitized paperOrother recording medium is carried upon a rotatable drum 23. Connectedto the drum through gears 24 and 25 is a. threaded shaft 26 along whichtravels a head 27, the head having an opening to receive stationary rod28 which restrains the head from turning with the shaft. Head 27 carriesa needle 29 for directing an electronic discharge to the sheet Wound ondrum This discharge is produced by an oscillat ng circuit 30 feedinginto circuit 31 containing coil 32 and condenser 33, the oscillatingcircuit being controlled by a suit able transmitting station such asdisclosed in the aforesaid application.

The oscillation circuit 85-85 l242 contains a modulating audion 342, anoscillating audion 88, battery 39 bridged by condenser 40, and aninductance coil 41 connccted at one end to grid 36 of the oscillatingaudion and at the other end, through battery 39, to the anode37 of theoscillating audion. The cathode d3 of the modulating audion is connectedto an intermediate point of coil at and the modulator anode or plate 44is connected to the oscillator cathode or filament 4-5. The potential onthe modulator grid 46 may be controlled in' any suitable way as forexample through transformer 47. A. condenser i8 may be connected betweenthe conductors and d2 by switch 49 but or djinariiy this condenser maybe dispensed wita.

With this arrangement the cathode-anode or plate circuit i242 of themodulating audion is in series With a part of the oscillating circuitand variation in the efiec-tive resistance of the modulator 3%, producedby variation in the potential of grid 46, produce opposite variation inthe amplitude of the oscillations. That is, increase of modulatorresistance decreases the amplitude of the 0s cillations.

By virtue of the aforesaid series connection of the modulating audionthe oscillations may be varied from maximum amplitude to zero amplitude,it being possible entirely to suppress the oscillations if desired byadjusting the potential of the grid (free grid potential) so that at onelimit of grid potential variation the efiectiv'e resistance of themodulating audion is high enough completely to stop the oscillations. Asecondary advantage of the series arrangement is that the single battery39 serves the plate circuits of both audions 1 uency and high-potentialadapted to produce an electronic discharge (e. g. a corona discharge)from needle 29 when above a predetermined intensity higher than thatexisting between successive impulses, the intensity of the dischargedepending upon the excess of oscillation intensit above thepredetermined intensity, where y an electronic discharge is emitted fromneedle 29 during each impulse (except perhaps While recording a white oran extremely light representation on the receiving paper). Thus, intransmitting a half-tone, a dot (or short dash) is recorded on thereceiving paper at each impulse, the dot varying inintensity in responseto variations in the intensity of said impulses, and in transmittingextreme contrasts such as the black and white of printed matter, at eachimpulse during passage of black or white (depending upon the adjustmentof the transmitting apparatus as above described) past the point ofincidence of the light from source 9.

The recording paper may be of the type requiring development subsequentto eX- posure by the electronic discharge to convert the latent imageinto a patent image or it may be of the type in which a patent image isproduced without development, the latter type having the advantage ofdisplaying the image as it is recorded. The electronic dischargeproduces the exposure as a result of its light and/or heat and/orelectronic bombardment of the photographic emulsion. If the recordingmedium is of the type adapted to be affected by the electronic dischargeindependently of the light produced thereby the paper may be enclosed inan opaque envelope or turned over and the process performed in a lightedroom, or a plurality of superposed sheets may be exposed simultaneously;and if the recording medium be of the type which is sensitive to theelectronic dischargebut insensitive to light the process may be carriedout in a lighted room without protecting the medium with an opaquecoverlIl i claim: 1. The art of photographic reproduction cal surfacewith a corona discharge, and varying the discharge in synchronism withthe subject matter transmitted.

3. Photographic reproduction apparatus comprising an electricaldischarge device, a high-frequency oscillator for producing a coronadischarge device from said device,

means for varying the amplitude of said discharge in accordance with thesubject matter to be reproduced, a support for the reproducing medium,and means for producing relative movement between said device andsupport so that the modulated discharge traces parallel paths 'acrosssaid medium.

4. Apparatus of the character described comprising an electricaldischarge device, means for continually producing a corona dischargefrom said device, means for varying the intensity of corona by thereceived impulses, a support for the receiving medium, and means forproducing relative movement between said device and support so that thevariable corona discharge moves over said medium in a predeterminedmanner.

5. In a photographic transmission system wherein the instantaneousvalues of propagated energy represent the various shades of the originalimpression and wherein reproduction is effected by local oscillations ona sensitized surface, the method of affecting the amplitude of theoscillations to produce a co rona of variable intensity at thesensitized surface whereby the tone color of the photograph isfaithfully reproduced.

6. Apparatus for electrical reproduction comprising a substantiallynon-conducting reproducing medium, and means for producing a coronadischarge in the medium to effect ionization in the medium by electronicaction without disruptive discharge.

Signed by me at Boston, Massachusetts, this 24th day of November, 1924.

. AUSTIN G. COOLEY.

